1. Field of the Invention
The present invention relates generally to anti-rotation devices used to prevent wear in the rotating control systems of helicopters and tilt rotor aircraft. Specifically, the present invention relates to a method and apparatus for limiting the rotation of an actuator rod used to manipulate the non-rotating swashplate of a swashplate system. The limitation of rotation prevents wear and structural damage to the actuator rod and the non-rotating swashplate.
2. Description of Related Art
Tilt rotor aircraft are hybrids between traditional helicopters and traditional propeller driven aircraft. Typical tilt rotor aircraft have fixed wings that terminate with convertible tilt rotor assemblies that house the engines and transmissions that drive the rotors. Tilt rotor aircraft are convertible from a helicopter mode, in which the tilt rotor aircraft can take-off, hover, and land like a helicopter; to an airplane mode, in which the tilt rotor aircraft can fly forward like a fixed-wing aircraft.
Helicopters and tilt rotor aircraft use rotating control systems. A rotating control system typically consists of a rotating swashplate and a non-rotating swashplate connected by a bearing system. The rotating swashplate tracks the movements of the non-rotating swashplate, and the angle of the main rotor blades are adjusted accordingly. The non-rotating swashplate is manipulated by the pilot by way of hydraulic actuators. Each actuator rod is attached to one of several devises of the non-rotating swashplate at a spherical bearing. The spherical bearing is held in place by a bearing housing at the end of the actuator rod.
The spherical bearing permits rotational misalignment of the actuator in all axes. The misalignment of the spherical bearing is determined and controlled by inputs from the flight control system. Rotation of the actuator about its own longitudinal axis is not restricted, nor can it be limited or controlled by inputs from the flight control system. Because of this condition, the bearing housing is able to rotate within the clevis such that it comes into contact with an inner surface of the clevis. Such contact causes wear resulting in structural damage to both the clevis arms and the bearing housing. Since the clevis arms are integral to the non-rotating swashplate, damage to the clevis arms compromises the structural integrity of the non-rotating swashplate. Damage to the non-rotating swashplate causes a hazardous condition that could cause a pilot to loose control of the helicopter or aircraft.
Due to the flight-critical nature of the non-rotating swashplate, there has been a desire to minimize wear and damage to the clevis arms. The solution to the problem in the past has been to install stainless steel wear pads between the bearing housing and the clevis arms. This approach does protect the clevis but does not protect the bearing housing, which is worn because of contact with the stainless steel pads. An additional problem is that the wear pads require frequent replacement, resulting in added costs and aircraft down time.
Although the stainless steel pads adequately protect the clevis, the problem of protecting both the clevis and the actuator rod bearing housing has not been adequately resolved.
There is a need for a tilt rotor aircraft having a rotating control system where the nonrotating swashplate clevis and actuator rod bearing housing are protected from wear and structural damage.
It is an object of the present invention to provide an anti-rotation clip for limiting the rotational freedom of an actuator rod so as to prevent contact between a bearing housing of the actuator rod and clevis arms of a clevis.
It is another object of the present invention to provide an anti-rotation clip having a sacrificial surface so as to minimize wear of the bearing housing.
It is yet another object of the present invention to provide an anti-rotation clip that prevents wear to the bearing housing and clevis arms without limiting the rotational misalignment capability of the spherical bearing.
It is yet another object of the present invention to provide an anti-rotation clip made of multipart construction, the multiple parts being assembled during installation of the clip into the clevis.
It is yet another object of the present invention to provide an anti-rotation clip made of unitary construction, the clip being adapted to be installed by compressing the sides of the clip, locating the clip in the clevis, and releasing the clip so that it snaps back to its original shape.
It is yet another object of the present invention to provide a method of preventing wear and structural damage in a rotating control system, whereby an anti-rotation clip is installed by compressing the sides of the clip, locating the clip in the clevis, and releasing the clip so that it snaps back to its original shape.
A principle advantage of the present invention is that the anti-rotation clip limits rotation of an actuator rod, thereby eliminating wear between a bearing housing and a swashplate clevis.
Another advantage of the present invention is that the anti-rotation clip, unlike prior art stainless steel wear pads, protects the flight-critical swashplate clevis and provides a sacrificial surface in order to prevent wear or damage to the bearing housing of the actuator rod.
Another advantage of the present invention is that in a multipart anti-rotation clip embodiment, the clip may be installed in certain applications without dismantling the actuator rod from the clevis arms.
The above objects, features, and advantages of the anti-rotation clip as well as additional objects, features, and advantages of the invention will become apparent in the following detailed description.